There is known a robot system with which an article being transferred by a transfer device is photographed with a camera to determine the position and orientation of the article, and a robot is track-controlled on the basis of the determined position and orientation and the article travel distance detected with an encoder so that the robot performs a task on the article while the article is being transferred (for example, refer to Japanese Unexamined Patent Application, Publication No. 2005-111607).
With this robot system, when detection of the position of the article fails, the robot system enters a next image capture preparation mode.